The present disclosure generally relates to well treatment fluid compositions and methods of use, and more particularly, to well treatment fluids and methods that include a delayed release percarbonate formulation.
The internal pressure in an oil well forces only about the first 3 percent to the surface and 10-20% can be acquired by traditional pumping. Gaining access to at least part of the remaining oil requires more advanced technology. In order to gain access, viscous well treatment fluids are commonly used in the drilling, completion, and treatment of subterranean formations penetrated by wellbores. For example, hydraulic fracturing is often practiced as a means to enhance recovery. During hydraulic fracturing, a viscous well treatment fluid is injected into a well bore under high pressure. Once the natural reservoir pressures are exceeded, the fracturing fluid initiates a fracture in the formation that generally continues to grow during pumping. As the fracture widens to a suitable width during the course of the treatment, a proppant (e.g., sand grains, aluminum pellets, or other material), may then also be added to the fluid. The proppant remains in the produced fracture to prevent closure of the fracture and to form a conductive channel extending from the well bore into the formation being treated once the fracturing fluid is recovered. The treatment design generally requires the well treatment fluid to reach a maximum viscosity as it enters the fracture that affects the fracture length and width. The viscosity of most fracturing fluids is generated from water-soluble polysaccharides, such as galactomannans or derivatives thereof. Crosslinking agents, such as borate, titanate, or zirconium ions, are commonly added to increase the fluid viscosity.
Once a suitable amount of fractures are formed, it is generally desirable that the fluid viscosity decrease to levels approaching that of water after the proppant is placed. This allows a portion of the treating fluid to be recovered without producing excessive amounts of proppant after the well is opened and returned to production. The recovery of the fracturing fluid is accomplished by reducing the viscosity of the fluid to a lower value such that it flows naturally from the formation. Incorporating chemical agents, referred to as breakers or breaking agents, into the fluid can accomplish this viscosity reduction or conversion. Typically, these agents are either oxidants or enzymes that operate to degrade the polymeric gel structure.
Treatment fluids are also utilized in sand control treatments, such as gravel packing. In gravel-packing treatments, a treatment fluid suspends particulates (commonly referred to as “gravel particulates”) for delivery to a desired area in a well bore, e.g., near unconsolidated or weakly-consolidated formation zones, to form a gravel pack to enhance sand control. One common type of gravel-packing operation involves placing a sand control screen in the well bore and packing the annulus between the screen and the well bore with the gravel particulates of a specific size to prevent the passage of formation sand. The gravel particulates act to prevent the formation particulates from occluding the screen or migrating with the produced hydrocarbons, and the screen acts to prevent the particulates from entering the production tubing. Once the gravel pack is substantially in place, the viscosity of the treatment fluid may be reduced to allow it to be recovered. In some situations, fracturing and gravel-packing treatments are combined into a single treatment (commonly referred to as “frac pack” operations). In such “frac pack” operations, the treatments are generally completed with a gravel pack screen assembly in place with the hydraulic fracturing treatment being pumped through the annular space between the casing and screen. In this situation, the hydraulic fracturing treatment may end in a tip screen-out condition. In other cases, the fracturing treatment may be performed prior to installing the screen and placing a gravel pack.
Maintaining sufficient viscosity in these treatment fluids is important for a number of reasons. Maintaining sufficient viscosity is important in fracturing and sand control treatments for particulate transport and/or to create or enhance fracture width. Also, maintaining sufficient viscosity may be important to control and/or reduce fluid-loss into the formation. Moreover, a treatment fluid of a sufficient viscosity may be used to divert the flow of fluids present within a subterranean formation (e.g., formation fluids, other treatment fluids) to other portions of the formation, for example, by “plugging” an open space within the formation. At the same time, while maintaining sufficient viscosity of the treatment fluid often is desirable, it also may be desirable to maintain the viscosity of the treatment fluid in such a way that the viscosity may be reduced at a particular time for subsequent recovery of the fluid from the formation. Additionally, the viscosity also may help determine the open fracture width.
In choosing a suitable breaker, one may consider the onset of the viscosity reduction, i.e., breakage. Viscous well treatment fluids that break prematurely can cause suspended proppant material to settle out before being introduced a sufficient distance into the produced fracture. Moreover, premature breaking can result in a less than desirable fracture width in the formation causing excessive injection pressures and premature termination of the treatment.
On the other hand, viscous well treatment fluids that break too slowly can cause slow recovery of the fracturing fluid from the produced fracture, which delays hydrocarbon production. Still further, the proppant can dislodge from the fracture, resulting in at least partial closing and decreased efficiency of the fracturing operation. Preferably, the fracturing gel should begin to break when the pumping operations are concluded. For practical purposes, the gel preferably should be completely broken within about 24 hours after completion of the fracturing treatment.
In low-temperature wells, enzymatic breaking agents are often used, but they are relatively expensive in comparison to oxizidizing breaking agents. In shallow wells, percarbonates are often used, but as the drilling gets deeper percarbonates provide premature breaking and are less preferred.
Accordingly, there is a need in the art for improved breaking agents that can be used in various settings, depths, conditions, and oil well applications.